Isoniazid resistance pattern among pulmonary tuberculosis patients in Bangladesh: An exploratory study.

Objectives: In high tuberculosis (TB) burden countries such as Bangladesh, research and policy tend to focus on rifampicin (RIF)-resistant TB patients, leaving RIF-sensitive but isoniazid (INH)-resistant (Hr-TB) patients undiagnosed. Our study aims to determine the prevalence of INH resistance among pulmonary TB patients in selected health care facilities in Bangladesh.

Methods: This study was conducted across nine TB Screening and Treatment Centres situated in Bangladesh. Sputum samples from 1084 Xpert-positive pulmonary TB patients were collected between April 2021 and December 2022 and cultured for drug susceptibility testing. Demographic and clinical characteristics of Hr-TB and drug-susceptible TB patients were compared.

Results: Among available drug susceptibility testing results of 998 culture-positive isolates, the resistance rate of any INH regardless of RIF susceptibility was 6.4% (64/998, 95% CI: 4.9-8.2). The rate was significantly higher in previously treated (21.1%, 16/76, 95% CI: 12.0-34.2) compared with newly diagnosed TB patients (5.2%, 48/922, 95% CI: 3.8-6.9) (p < 0.001). The rate of Hr-TB was 4.5% (45/998, 95% CI: 3.3-6.0), which was also higher among previously treated patients (6.6%, 5/76, 95% CI: 1.4-13.5) compared with newly diagnosed TB patients (4.3%; 40/922, 95% CI: 3.1-5.9) (p 0.350). Most importantly, the rate of Hr-TB was more than double compared with MDR-TB (4.5%, 45/998, vs. 1.9%, 19/998) found in the current study.

Discussion: This study reveals a high prevalence of Hr-TB, surpassing even that of the multi-drug-resistant TB in Bangladesh. This emphasizes the urgent need to adopt WHO-recommended molecular tools at the national level for rapid detection of INH resistance so that patients receive timely and appropriate treatment.